The technology described herein relates to a method of and an apparatus for processing frames for provision on an electronic display.
It is common for electronic devices, such as mobile phones, and for data processing systems in general, to include some form of electronic display screen, such as an LCD panel. To display an image on the display, the pixels (picture elements) or sub-pixels of the display must be set to appropriate colour values. This is usually done by generating and storing in memory a frame of data to be displayed which indicates, for each pixel or sub-pixel, the colour value to be displayed.
Many electronic display screens such as LCD panels, for example, use a backlight to illuminate the screen for viewing. However, it is known that using a backlight is significantly burdensome on an electronics device's total power consumption. To reduce the power consumption of the backlight of a display screen, the intensity (absolute brightness) of the backlight is reduced, as it is known that the intensity of the backlight is proportional to its power consumption.
An issue with lowering the backlight intensity is that it also reduces the luminance (brightness) of the image being displayed, compared to the luminance at which the image was intended to be displayed.
Various methods have accordingly been developed to optimise the display when dimming the backlight. One such method is called “luminance and backlight scaling”, which involves scaling (modifying) the luminance of the image itself to compensate for dimming the backlight.
Backlight and luminance scaling operation typically involves analysing the frame buffer data (e.g. by use of a histogram) to determine an optimum backlight dimming factor and luminance scaling parameters.
Luminance and backlight scaling includes a method called “luminance compensation” which involves recovering at least some of the image luminance that is lost when dimming the backlight by increasing the luminance of the image with respect to a high threshold value.
Other terms for luminance compensation include Brightness Compensation and Image Compensation. For convenience the term luminance compensation will be used herein, but it will be understood that this is intended to include and encompass all equivalent terms and techniques.
FIGS. 1a and 1b illustrate the general principles behind luminance compensation operation.
FIG. 1a shows an image 11 that is being displayed on a display and a histogram 12 showing the density distribution 13 of the display sub-pixels across all of their possible luminance values. In this example, the backlight is set at 100% intensity and luminance compensation is not used. (As can be seen in FIG. 1a, an 8-bit value (corresponding to 256 shades of luminance) is used for each sub-pixel.)
FIG. 1b shows the same image 11 and corresponding histogram 15 as that of FIG. 1a, except that in the example of FIG. 1b the backlight intensity is reduced to 70%. As can be seen in FIG. 1b, in order to compensate for the image luminance that is lost when dimming the backlight, the luminance values of the sub-pixels have been boosted (e.g. by applying an appropriate transformation function to the original frame buffer data). This is reflected by FIG. 1b which shows that the density distribution 14 of the display sub-pixels is concentrated at higher luminance values.
Luminance and backlight scaling may also include a method called “image enhancement”, which involves modifying the frame buffer data so as to increase the contrast of the image when the backlight is dimmed. Image enhancement typically involves applying a transformation function to the original frame buffer data so as to remap the luminance of the pixels or sub-pixels with respect to a high and low threshold value.
Other terms used for image enhancement include Contrast Enhancement, Histogram Equalisation and Histogram Stretching. For convenience the term image enhancement will be used herein, but it will be understood that this is intended to include and encompass all equivalent terms and techniques.
FIG. 2 illustrates an exemplary data processing system with luminance and backlight scaling operation.
As shown in FIG. 2, the data processing system includes a central processing unit (CPU) 23, a graphics processing unit (GPU) 24, a video engine 25, a display controller 27, and an image processing engine such as a luminance and backlight scaling engine 26 that communicate via an interconnect 212 in a system-on-chip (SoC) arrangement 21. The CPU, GPU, video engine, display controller and luminance and backlight scaling engine also have access to off-chip memory 211 for storing, inter alia, frames, via a memory controller 210.
The system also includes a display arrangement 22, comprising a backlight 28 and a display 29. The luminance and backlight scaling engine 26 sets the brightness of the backlight 28, and the display controller 27 provides output frames for display to the display 29.
When a frame is to be displayed, the GPU 24 and/or video engine 25 will, for example, generate a frame for display which will then be stored, via the memory controller 210, in a frame buffer in the off-chip memory 211.
When the frame is to be displayed, the luminance and backlight scaling engine 26 will then read the frame from the frame buffer and analyse the frame buffer data (e.g. by use of a histogram) to determine an optimum backlight dimming factor and dynamic luminance scaling parameters.
Following this determination, the luminance and backlight scaling engine 26 will modify the frame buffer data so as to generate a modified, luminance scaled output frame for display. The luminance and backlight scaling engine 26 will then set the backlight level(s) at the determined intensity and the display controller 27 will provide the modified, luminance scaled output frame to the display 29 for display.
The Applicants believe that there remains scope for improvements to methods of and apparatus for processing a frame for provision on a display.
Like reference numerals are used for like features throughout the drawings, where appropriate.